Septic Systems

Septic system basics

Most septic systems are a simple design with a two compartment tank and drain field. The septic tank is a watertight box, usually made of concrete or fiberglass, with an inlet and outlet pipe. The septic tank treats the wastewater by holding it in the tank long enough for solids and liquids to separate. 
Septic Drainfield

Sludge and scum

Solids lighter than water (such as fats, oils, and grease) float to the top forming a layer of scum. Solids heavier than water settle at the bottom of the tank forming a layer of sludge. The layers of sludge and scum remain in the septic tank where bacteria found naturally in the wastewater work to break the solids down. The sludge and scum that can't be broken down are retained in the tank until it is pumped.


tandard drain field

A standard drain field is a series of trenches or a bed lined with gravel or course sand and buried 1' - 3' below the ground's surface. Perforated pipes or drain tiles run through the trenches to distribute the wastewater. The drain field treats the wastewater by allowing it to slowly trickle from the pipes out into the gravel and down through the soil.

Caring for your septic system

There are many ways to extend the life and functionality of your septic system

Have your septic system inspected

Your septic system needs an annual inspection and needs to be pumped at least every three years, or more frequently depending on what type of system you have. 

Be smart when you hire a septic contractor

Check out the Labor & Industries website to learn how to "hire smart" and protect your home in the process.

Learn how to be SepticSmart

Check out EPA's "Dos and Don'ts" of your septic system to protect your home, health, environment, and property value at

Questions about connecting to sewer? 

Contact our Development Review Engineer.

Questions about our septic program? 

Contact our Surface Water Program Coordinator.